1. Field of the Invention
The present invention relates to a variable valve actuator and, more particularly, to a variable valve actuator, in which the lift time and the lift distance of a valve are varied according to the low-/high-speed operating range of an engine.
2. Description of the Related Art
As for an engine, a camshaft is rotated by a rotating force transmitted from a crank shaft, and an intake valve and an exhaust valve are reciprocated up and down with regular timing by cams of the camshaft. Thereby, intake air is supplied to a combustion chamber, and then combustion gas is exhausted. In this process, a fuel-air mixture is compressed and exploded to generate power.
In this manner, a series of elements such as a drive cam, a camshaft, a tappet, a rocker arm, etc. for operating the intake and exhaust valves is called a valve train.
This valve train will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a side view illustrating a conventional valve train.
As illustrated in FIG. 1, the conventional valve train includes drive cams 12, a camshaft 11, rocker arms 14 and valves 15. The drive cams 12 are coupled to the camshaft 11 at predetermined intervals, and each rocker arm 14 making angular motion with respect to a pivot pin 13 is installed under the corresponding drive cam 12.
Further, the intake port or the exhaust port of a cylinder head is disposed below an outer end of each rocker arm 14 with the valve 15 elastically supported by a valve spring 16. Thus, when the camshaft 11 is rotated, rollers 14a of the rocker arms 14 are pushed up and down by the respective drive cams 12 having different radii of rotation. Then, each rocker arm 14 makes angular motion with respect to the corresponding pivot pin 13, and the outer end of each rocker arm 14 applies force to a stem end part of the corresponding valve 15. Thus, the valve 15 is lowered against an elastic force of the valve spring 16. Meanwhile, when a position of each drive cam 12 is changed and thus each rocker arm 14 makes angular motion in an upward direction, the corresponding valve 15 is again raised by the elastic force of the valve spring 16.
In this manner, the intake and exhaust valves are repeatedly opened and closed at regular intervals by the operation of the valve train 10.
However, this ordinary valve train makes a single degree-of-freedom system motion by motion of the cam, so that it is impossible to change the valve train depending on engine operation conditions such as high-speed and low-speed engine operation conditions.
In order to solve this problem, there have been developed a variety of variable valve actuators, each of which is adapted to adjust a lift time and a lift distance of the valve 15 according to the engine speed. However, these variable valve actuators must change positions of the drive cams 12 and the camshaft 11, so that it is difficult to easily apply them to existing mass-produced engines.
Further, these variable valve actuators are designed to merely adjust the lift time of the valve 15 by increasing or decreasing the lift distance of the valve 15, so that it is impossible to more efficiently adjust the lift time of the valve 15.
In addition, the variable valve actuators additionally require separate variable cams in addition to the drive cams 12 coupled to the camshaft 11 in order to adjust the lift distance and the lift time of the valve 15. In this manner, because each valve 15 is equipped with the drive cam 12 and the variable cam, the variable valve actuators have complicated internal configuration.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.